EP1590782A1 - Electrophoretic display panel - Google Patents

Electrophoretic display panel

Info

Publication number
EP1590782A1
EP1590782A1 EP04701654A EP04701654A EP1590782A1 EP 1590782 A1 EP1590782 A1 EP 1590782A1 EP 04701654 A EP04701654 A EP 04701654A EP 04701654 A EP04701654 A EP 04701654A EP 1590782 A1 EP1590782 A1 EP 1590782A1
Authority
EP
European Patent Office
Prior art keywords
picture element
particles
display panel
actual position
electrode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP04701654A
Other languages
German (de)
French (fr)
Inventor
Mark T. Johnson
Alexander V. Henzen
Hugo J. Cornelissen
Guofu Zhou
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips Electronics NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics NV filed Critical Koninklijke Philips Electronics NV
Priority to EP04701654A priority Critical patent/EP1590782A1/en
Publication of EP1590782A1 publication Critical patent/EP1590782A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/3433—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices
    • G09G3/344—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices based on particles moving in a fluid or in a gas, e.g. electrophoretic devices
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
    • G02F1/166—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
    • G02F1/167—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
    • G02F1/1675—Constructional details
    • G02F1/1676—Electrodes
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
    • G02F1/1685—Operation of cells; Circuit arrangements affecting the entire cell
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
    • G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
    • G09F9/37—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being movable elements
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
    • G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
    • G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
    • G09F9/37—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being movable elements
    • G09F9/372—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being movable elements the positions of the elements being controlled by the application of an electric field
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
    • G02F2201/12—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 electrode
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/0233—Improving the luminance or brightness uniformity across the screen
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/029—Improving the quality of display appearance by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/3433—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices
    • G09G3/344—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices based on particles moving in a fluid or in a gas, e.g. electrophoretic devices
    • G09G3/3446—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices based on particles moving in a fluid or in a gas, e.g. electrophoretic devices with more than two electrodes controlling the modulating element

Definitions

  • the invention relates to an electrophoretic display panel for displaying a picture corresponding to image information, comprising:
  • an electrophoretic medium comprising charged particles in a fluid
  • the charged particles being able to occupy a position between the electrodes
  • the drive means being able to control for each picture element the potentials, thereby being able to change the position of the particles based on the image information
  • the monitoring means being able to generate for each picture element actual position information indicative for the actual position of the particles
  • the control means being able to control for each picture element the drive means in dependence of the actual position information and the image information to reduce a difference between the actual position of the particles and the position of the particles corresponding to the image information.
  • the monitoring means also register the intensity of ambient light falling onto the display panel and comprise to that end a plurality of photo sensors arranged around the periphery of the display panel. If the registered intensity of the ambient light penetrated into each picture element is compared with the registered intensity of the ambient light falling onto the display panel, the registered intensity of each picture element is indicative for the actual position of the particles in each picture element.
  • the control means control for each picture element the drive means in dependence of the registered intensities and the image information to reduce the difference between the actual position of the particles and the position of the particles corresponding to the image information.
  • the difference between the actual picture on the display panel and the intended picture on the display panel being an exact representation of the image information, is relatively small. Therefore, the actually displayed picture has a relatively high quality.
  • the photo sensors inaccurately register the intensity of the ambient light. As a result, the actually displayed picture then has a rather poor picture quality.
  • the particles occupying a position near the first electrode may correspond to the same value of the resistance as the particles occupying a position near the second electrode.
  • Monitoring of the actual position of the particles by means of the electrical resistance can be improved by a combination of the electrical resistance and a function of a derivative of the resistance with respect to the position of the particles in the picture element. Therefore, in an embodiment, the electrical means are able to generate for each picture element the actual position information based on an electrical resistance between the first and the second electrode and a function of a derivative of the resistance with respect to the position of the particles of the respective picture element.
  • the function is a sign function, being positive for a positive value, zero for a zero value and negative for a negative value, which can relatively easy be determined.
  • the electrical means are able to generate for each picture element the actual position information based on a capacitance between the first and the second electrode and a function of a derivative of the capacitance with respect to the position of the particles of the respective picture element.
  • the function is a sign function, which can relatively easy be determined.
  • Figure 1 shows diagrammatically a front view of an embodiment of the display panel
  • Figure 2 shows diagrammatically a cross-sectional view along II-II in Figure l;
  • Figure 3 shows in a graphical form the relation between the position X of the particles and the electrical resistance R;
  • Figure 4 shows diagrammatically a cross-sectional view along II-II in Figure 1 of a second embodiment;
  • Figure 5 shows in a graphical form the relation between the position X of the particles and the capacitance C.
  • Figure 6 shows diagrammatically a cross-sectional view along II-II in Figure 1 of a third embodiment
  • Figures 1 and 2 show the embodiment of the display panel 1 having a first substrate 8, a second opposed substrate 9 and a plurality of picture elements 2.
  • the picture elements 2 are arranged along substantially straight lines in a two-dimensional structure. Other arrangements of the picture elements 2 are alternatively possible, e.g. a honeycomb arrangement.
  • An electrophoretic medium 5, having charged particles 6 in a fluid, is present between the substrates 8,9.
  • a first and a second electrode 3,4 are associated with each picture element 2 for receiving a first and a second potential, respectively.
  • the first substrate 8 has for each picture element 2 a first electrode 3
  • the second substrate 9 has for each picture element 2 a second electrode 4.
  • the appearance of the picture element 2 is black.
  • the picture element 2 has one of the intermediate appearances, e.g. light gray, middle gray and dark gray, which are gray levels between white and black.
  • the drive means 100 are able to control for each picture element 2 the potentials, thereby being able to change the position of the particles 6.
  • the monitoring means 101 are able to generate for each picture element 2 actual position infonnation indicative for the position of the particles 6.
  • the monitoring means 101 have electrical means 102 which are able to generate for each picture element 2 the actual position information based on an electrical property of the respective picture element 2.
  • the control means 103 are able to control for each picture element 2 the drive means 100 in dependence of the actual position information and the image infonnation to reduce a difference between the actual position of the particles 6 and the position of the particles 6 corresponding to the image information.
  • the particles 6 in a picture element 2 occupy a position corresponding to an actual appearance of the picture element 2 which is light gray.
  • the monitoring means 101 generate actual position information indicating that the picture element 2 is light gray.
  • the picture appearance being the appearance of the picture element 2 determined by the position of the particles 6 corresponding to the image information, is dark gray.
  • the control means 101 control the drive means 100 to have the first and the second electrode 3,4 receive a first potential which is e.g. 15 Volts smaller than the second potential for an interval depending on the change of appearance which has to be achieved.
  • the monitoring means 101 generate again actual position information, used by the control means, etc. resulting in a further reduction of the difference between the actual appearance and the picture appearance.
  • the electrical means 102 are able to generate for each picture element 2 the actual position information based on the electrical resistance between the first and the second electrode 3,4.
  • Figure 3 shows an example of the relation between the position X of the particles 6 and the electrical resistance R, in the case that the particles have a higher resistance than the fluid.
  • position IP1 corresponds to the picture element 2 having a light gray appearance, denoted by LG, and a value R2 of the electrical resistance
  • position IP2 corresponds to the picture element 2 having a middle gray appearance, denoted by MG
  • a value R3 of the electrical resistance and position IP3 corresponds to the picture element 2 having a dark gray appearance, denoted by DG
  • a value R2 of the electrical resistance When the particles 6 occupy one of the extreme positions the electrical resistance is relatively large compared to the particles 6 occupying one of the intermediate positions.
  • the actual position of the particles 6 in a picture element is position EP1, corresponding to the picture element 2 having a white appearance and a value of the electrical resistance being Rl.
  • the electrical means 101 generate actual position information from the value Rl of the resistance indicating that the picture element 2 is white.
  • the picture appearance is light gray, denoted by LG.
  • the control means 101 control the drive means 100 to reduce the difference between the actual appearance and the picture appearance. As a result, the difference between the actual appearance and the picture appearance is reduced and the picture element 2 has become darker.
  • the electrical means 102 are able to generate for each picture element 2 the position information based on the electrical resistance between the first and the second electrode 3,4 and a function of the derivative of the resistance with respect to the position of the particles 6 of the respective picture element 2.
  • the relation between the resistance R and the position X of the particles 6 shows that one value of the resistance may relate to two different positions of the particles 6.
  • the particles 6 occupying position IP1 corresponding to a picture element 2 having a light gray appearance result in the same electrical resistance, R2, as the particles 6 occupying position IP3 corresponding to a picture element 2 having a dark gray appearance.
  • Figure 3 also shows that monitoring of the actual position of the particles by means of the electrical resistance can be improved by the combination of the resistance R and a function of the derivative of the resistance R with respect to the position of the particles 6.
  • the derivative of the resistance with respect to the position of the particles 6 has a negative sign
  • the derivative of the resistance with respect to the position of the particles 6 has a positive sign
  • the electrical property is the capacitance between the first electrode 3 and the second electrode 4.
  • the second substrate 9 has for each picture element 2 the first electrode 3 and the second electrode 4.
  • position IPl corresponds to the picture element 2 having a light gray appearance
  • position IP2 corresponds to the picture element 2 having a dark gray appearance
  • a " value C3 of the capacitance and position IP3 corresponds to the picture element 2 having a black appearance
  • a value C4 of the capacitance When the particles 6 occupy one of the extreme positions the capacitance is relatively low compared to the particles 6 occupying one of the intermediate positions.
  • the electrical means 102 may be able to determine the capacitance C from the registration of the time required to reach a predetermined voltage difference between the first and the second electrode 3,4 as a consequence of the application of a predetermined current between the first and the second electrode 3,4. It is favorable, if the predetermined current is present only for a relatively short time, as a then the position of the particles 6 is substantially unchanged.
  • the electrical means 102 are able to generate for each picture element 2 the position information based on the capacitance between the first and the second electrode 3,4 and a function of the derivative of the capacitance with respect to the position of the particles 6 of the respective picture element 2.
  • the relation between the capacitance C and the position X of the particles 6 shows that one value of the capacitance may relate to two different positions of the particles 6.
  • Figure 5 also shows that monitoring of the actual position of the particles by means of the capacitance can be improved by the combination of the capacitance C and a function of the derivative of the capacitance C with respect to the position of the particles 6, similarly as is described with the resistance R and the derivative of the resistance.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Optics & Photonics (AREA)
  • Computer Hardware Design (AREA)
  • Molecular Biology (AREA)
  • Electrochemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)

Abstract

The electrophoretic display panel (1) for displaying a picture corresponding to image information has drive means (100) which are able to control for each picture element (2) the potentials, thereby being able to change the position of the particles (6) based on the image information. Furthermore, the display panel (1) has monitoring means (101) which are able to generate for each picture element (2) actual position information indicative for the actual position of the particles (6), and control means (103) which are able to control for each picture element (2) the drive means (100) in dependence of the actual position information and the image information to reduce a difference between the position of the particles (6) and the position off the particles (6) corresponding to the image information. For the display panel (1) to be able to provide a picture of relatively high quality even at relatively low or non­uniform intensities of the ambient light, the monitoring means (101) comprise electrical means (102) which are able to generate for each picture element (2) the actual position information based on an electrical property of the respective picture element (2).

Description

Electrophoretic display panel
The invention relates to an electrophoretic display panel for displaying a picture corresponding to image information, comprising:
- an electrophoretic medium, comprising charged particles in a fluid;
- a plurality of picture elements; - a first and a second electrode associated with each picture element for receiving a first and a second potential, respectively,
- drive means;
- monitoring means; and
- control means, the charged particles being able to occupy a position between the electrodes, the drive means being able to control for each picture element the potentials, thereby being able to change the position of the particles based on the image information, the monitoring means being able to generate for each picture element actual position information indicative for the actual position of the particles, and the control means being able to control for each picture element the drive means in dependence of the actual position information and the image information to reduce a difference between the actual position of the particles and the position of the particles corresponding to the image information.
An embodiment of the electrophoretic display panel of the type mentioned in the opening paragraph is described in non-prepublished European Patent application 02077045.9 (PHNL020386).
In electrophoretic display panels in general, the picture elements have, during the display of the picture, appearances determined by the positions of the charged particles between the electrodes. The positions of the particles depend, however, not only on the potentials but also on the history of the potentials. As a result, the picture being displayed corresponding to the image information differs significantly from an exact representation of the image information. Therefore, the picture being displayed has a relatively low quality. The dependency on the history is reduced in the described electrophoretic display panel in the following way. The monitoring means, comprising a photo sensor in each picture element, register the intensity of ambient light penetrated into each picture element. The level of absorption of the ambient light depends on the position of the particles. The monitoring means also register the intensity of ambient light falling onto the display panel and comprise to that end a plurality of photo sensors arranged around the periphery of the display panel. If the registered intensity of the ambient light penetrated into each picture element is compared with the registered intensity of the ambient light falling onto the display panel, the registered intensity of each picture element is indicative for the actual position of the particles in each picture element. The control means control for each picture element the drive means in dependence of the registered intensities and the image information to reduce the difference between the actual position of the particles and the position of the particles corresponding to the image information. As a result, the difference between the actual picture on the display panel and the intended picture on the display panel, being an exact representation of the image information, is relatively small. Therefore, the actually displayed picture has a relatively high quality. However, at relatively low or non-uniform intensities of the ambient light, the photo sensors inaccurately register the intensity of the ambient light. As a result, the actually displayed picture then has a rather poor picture quality.
It is a drawback of the described display panel that the actually displayed picture has a rather poor quality at relatively low or non-uniform intensities of the ambient light.
It is an object of the invention to provide a display panel of the kind mentioned in the opening paragraph which is able to provide a picture of relatively high quality even at relatively low or non- uniform intensities of the ambient light.
The object is thereby achieved that the monitoring means comprise electrical means able to generate for each picture element the actual position information based on an electrical property of the respective picture element. The invention is based on the insight that, if, for each picture element, the actual position information is based on an electrical property of the respective picture element, the actual position information obtained is independent of the intensity of the ambient light. The electrical property may for instance be the electrical resistance between the first and the second electrode as the electrical conductivity of the particles is different than the electrical conductivity of the fluid. Therefore, the electrical resistance depends on the position of the particles. Therefore, in an embodiment, the electrical means are able to generate for each picture element the actual position information based on an electrical resistance between the first and the second electrode. However, a value of the resistance may relate to two different positions of the particles. As an example, the particles occupying a position near the first electrode may correspond to the same value of the resistance as the particles occupying a position near the second electrode. Monitoring of the actual position of the particles by means of the electrical resistance can be improved by a combination of the electrical resistance and a function of a derivative of the resistance with respect to the position of the particles in the picture element. Therefore, in an embodiment, the electrical means are able to generate for each picture element the actual position information based on an electrical resistance between the first and the second electrode and a function of a derivative of the resistance with respect to the position of the particles of the respective picture element. In a variation, the function is a sign function, being positive for a positive value, zero for a zero value and negative for a negative value, which can relatively easy be determined.
In another embodiment the electrical means are able to generate for each picture element the actual position information based on a capacitance between the first electrode and the second electrode, as the capacitance depends on the position of the charged particles as the particles and the fluid have different dielectric constants. However, a value of the capacitance may relate to two different positions of the particles. As an example, the particles occupying a position near the first electrode may correspond to the same value of the capacitance as the particles occupying a position near the second electrode. Monitoring of the actual position of the particles by means of the capacitance can be improved by a combination of the capacitance and a function of a derivative of the capacitance with respect to the position of the particles in the picture element. Therefore, in an embodiment the electrical means are able to generate for each picture element the actual position information based on a capacitance between the first and the second electrode and a function of a derivative of the capacitance with respect to the position of the particles of the respective picture element. In a variation, the function is a sign function, which can relatively easy be determined. These and other aspects of the display panel of the invention will be further elucidated and described with reference to the drawings, in which:
Figure 1 shows diagrammatically a front view of an embodiment of the display panel;
Figure 2 shows diagrammatically a cross-sectional view along II-II in Figure l;
Figure 3 shows in a graphical form the relation between the position X of the particles and the electrical resistance R; Figure 4 shows diagrammatically a cross-sectional view along II-II in Figure 1 of a second embodiment;
Figure 5 shows in a graphical form the relation between the position X of the particles and the capacitance C; and
Figure 6 shows diagrammatically a cross-sectional view along II-II in Figure 1 of a third embodiment; and
In all the Figures corresponding parts are referenced to by the same reference numerals.
Figures 1 and 2 show the embodiment of the display panel 1 having a first substrate 8, a second opposed substrate 9 and a plurality of picture elements 2. Preferably, the picture elements 2 are arranged along substantially straight lines in a two-dimensional structure. Other arrangements of the picture elements 2 are alternatively possible, e.g. a honeycomb arrangement. An electrophoretic medium 5, having charged particles 6 in a fluid, is present between the substrates 8,9. A first and a second electrode 3,4 are associated with each picture element 2 for receiving a first and a second potential, respectively. In Figure 2 the first substrate 8 has for each picture element 2 a first electrode 3, and the second substrate 9 has for each picture element 2 a second electrode 4. The charged particles 6 are able to occupy extreme positions near the electrodes 3,4 and intermediate positions in between the electrodes 3,4. Each picture element 2 has an appearance detennined by the position of the charged particles 6 between the electrodes 3,4. Electrophoretic media 5 are known per se from e.g. US 5,961,804, US 6,120,839 and US 6,130,774 and can e.g. be obtained from E Ink Corporation. As an example, the electrophoretic medium 5 comprises negatively charged black particles 6 in a white fluid. When the charged particles 6 are in a first extreme position, i.e. near the first electrode 3, as a result of the first potential being e.g. 15 Volts larger than the second potential, the appearance of the picture element 2 is e.g. white. When the charged particles 6 are in a second extreme position, i.e. near the second electrode 4, due to a potential difference between the first and the second electrode of opposite polarity, i.e. -15 Volts, the appearance of the picture element 2 is black. When the charged particles 6 are in one of the intermediate positions, i.e. in between the electrodes 3,4, the picture element 2 has one of the intermediate appearances, e.g. light gray, middle gray and dark gray, which are gray levels between white and black. The drive means 100 are able to control for each picture element 2 the potentials, thereby being able to change the position of the particles 6. The monitoring means 101 are able to generate for each picture element 2 actual position infonnation indicative for the position of the particles 6. The monitoring means 101 have electrical means 102 which are able to generate for each picture element 2 the actual position information based on an electrical property of the respective picture element 2. The control means 103 are able to control for each picture element 2 the drive means 100 in dependence of the actual position information and the image infonnation to reduce a difference between the actual position of the particles 6 and the position of the particles 6 corresponding to the image information.
As an example, the particles 6 in a picture element 2 occupy a position corresponding to an actual appearance of the picture element 2 which is light gray. The monitoring means 101 generate actual position information indicating that the picture element 2 is light gray. In this example, the picture appearance, being the appearance of the picture element 2 determined by the position of the particles 6 corresponding to the image information, is dark gray. To reduce the difference between the actual appearance and the picture appearance, the control means 101 control the drive means 100 to have the first and the second electrode 3,4 receive a first potential which is e.g. 15 Volts smaller than the second potential for an interval depending on the change of appearance which has to be achieved. As a result, the difference between the actual appearance and the picture appearance is reduced, in this case the picture element 2 has become darker. Preferably, the monitoring means 101 generate again actual position information, used by the control means, etc. resulting in a further reduction of the difference between the actual appearance and the picture appearance.
In an embodiment the electrical means 102 are able to generate for each picture element 2 the actual position information based on the electrical resistance between the first and the second electrode 3,4. Figure 3 shows an example of the relation between the position X of the particles 6 and the electrical resistance R, in the case that the particles have a higher resistance than the fluid. When the particles 6 occupy the first extreme position, denoted by EP1, corresponding to a picture element 2 having a white appearance, denoted by W, the value of the electrical resistance is Rl. When the particles 6 occupy the second extreme position, denoted by EP2, corresponding to the picture element 2 having a black appearance, denoted by B, the value of the electrical resistance is Rl. The intermediate positions are denoted by IP, e.g. position IP1 corresponds to the picture element 2 having a light gray appearance, denoted by LG, and a value R2 of the electrical resistance, position IP2 corresponds to the picture element 2 having a middle gray appearance, denoted by MG, and a value R3 of the electrical resistance and position IP3 corresponds to the picture element 2 having a dark gray appearance, denoted by DG, and a value R2 of the electrical resistance. When the particles 6 occupy one of the extreme positions the electrical resistance is relatively large compared to the particles 6 occupying one of the intermediate positions. As an example the actual position of the particles 6 in a picture element is position EP1, corresponding to the picture element 2 having a white appearance and a value of the electrical resistance being Rl. The electrical means 101 generate actual position information from the value Rl of the resistance indicating that the picture element 2 is white. In this example, the picture appearance is light gray, denoted by LG. Then the control means 101 control the drive means 100 to reduce the difference between the actual appearance and the picture appearance. As a result, the difference between the actual appearance and the picture appearance is reduced and the picture element 2 has become darker.
In another embodiment the electrical means 102 are able to generate for each picture element 2 the position information based on the electrical resistance between the first and the second electrode 3,4 and a function of the derivative of the resistance with respect to the position of the particles 6 of the respective picture element 2. As an example refer to Figure 3. The relation between the resistance R and the position X of the particles 6 shows that one value of the resistance may relate to two different positions of the particles 6. In this example, the particles 6 occupying position IP1 corresponding to a picture element 2 having a light gray appearance result in the same electrical resistance, R2, as the particles 6 occupying position IP3 corresponding to a picture element 2 having a dark gray appearance. Figure 3 also shows that monitoring of the actual position of the particles by means of the electrical resistance can be improved by the combination of the resistance R and a function of the derivative of the resistance R with respect to the position of the particles 6. In this example, for the position of the particles 6 corresponding to the picture element 2 having a light gray appearance, the derivative of the resistance with respect to the position of the particles 6 has a negative sign, whereas for the position of the particles 6 corresponding to a picture element 2 having a dark gray appearance the derivative of the resistance with respect to the position of the particles 6 has a positive sign. In another embodiment the electrical property is the capacitance between the first electrode 3 and the second electrode 4. As an example, see Figure 4, the second substrate 9 has for each picture element 2 the first electrode 3 and the second electrode 4. The electrical means 102 are able to determine the capacitance between the first electrode 3 and the second electrode 4. Figure 5 shows an example of the relation between the position X of the particles 6 and the capacitance C, in the case that the particles 6 have a higher dielectric constant than the fluid. When the particles 6 occupy the first extreme position, corresponding to a picture element 2 having a white appearance, the value of the capacitance is Cl. When the particles 6 occupy the second extreme position, also corresponding to the picture element 2 having a white appearance, the value of the capacitance is Cl. The intermediate positions are denoted by IP, e.g. position IPl corresponds to the picture element 2 having a light gray appearance, and a value C2 of the capacitance, position IP2 corresponds to the picture element 2 having a dark gray appearance, and a" value C3 of the capacitance and position IP3 corresponds to the picture element 2 having a black appearance, and a value C4 of the capacitance. When the particles 6 occupy one of the extreme positions the capacitance is relatively low compared to the particles 6 occupying one of the intermediate positions. The electrical means 102 may be able to determine the capacitance C from the registration of the time required to reach a predetermined voltage difference between the first and the second electrode 3,4 as a consequence of the application of a predetermined current between the first and the second electrode 3,4. It is favorable, if the predetermined current is present only for a relatively short time, as a then the position of the particles 6 is substantially unchanged.
In another embodiment the electrical means 102 are able to generate for each picture element 2 the position information based on the capacitance between the first and the second electrode 3,4 and a function of the derivative of the capacitance with respect to the position of the particles 6 of the respective picture element 2. As an example refer to Figure 5. The relation between the capacitance C and the position X of the particles 6 shows that one value of the capacitance may relate to two different positions of the particles 6. Figure 5 also shows that monitoring of the actual position of the particles by means of the capacitance can be improved by the combination of the capacitance C and a function of the derivative of the capacitance C with respect to the position of the particles 6, similarly as is described with the resistance R and the derivative of the resistance.
In another embodiment shown in Figure 6, the second substrate 9 has the first electrodes 3, the second electrodes 4 and, furthermore, the second substrate 9 has for each picture element 2 a third electrode 7 for receiving a third potential. The part of the picture element 2 related to the second and the third electrodes 4,7 may act as reservoir for the particles 6, shielded from the viewer. The appearance of the picture element 2 is determined by the position of the particles 6 between the first and the second electrodes 3,4. The three electrodes 3,4,7 determine the number of the particles 6 present between the first and the second electrode 3,4 and the position of the particles 6 between the first and the second electrode 3,4. The electrical means 102 are able to generate for each picture element 2 the actual position information based on the capacitance C between the first electrode 3 and the second electrode 4 and a further capacitance between the second electrode 4 and the third electrode 7. In a similar way as described above, the electrical means 102 may be able to determine the further capacitance.

Claims

CLAIMS:
1. An electrophoretic display panel (1) for displaying a picture corresponding to image information, comprising:
- an electrophoretic medium (5), comprising charged particles (6) in a fluid;
- a plurality of picture elements (2); - a first and a second electrode (3,4) associated with each picture element (2) for receiving a first and a second potential, respectively,
- drive means (100);
- monitoring means (101) ; and
- control means (103) , the charged particles (6) being able to occupy a position between the electrodes (3,4), the drive means (100) being able to control for each picture element (2) the potentials, , . thereby being able to change the position of the particles (6) based on the image information, the monitoring means (101) being able to generate for each picture element (2) actual position information indicative for the actual position of the particles (6), and the control means (103) being able to control for each picture element (2) the drive means (100) in dependence of the actual position information and the image information to reduce a difference between the actual position of the particles (6) and the position of the particles (6) corresponding to the image information, characterized in that the monitoring means (101) comprise electrical means (102) able to generate for each picture element (2) the actual position information based on an electrical property of the respective picture element (2).
2. A display panel (1) as claimed in claim 1 characterized in that the electrical means (102) are able to generate for each picture element (2) the actual position information based on an electrical resistance between the first and the second electrode (3,4).
3. A display panel (1) as claimed in claim 1 characterized in that the electrical means (102) are able to generate for each picture element (2) the actual position information based on an electrical resistance between the first and the second electrode (3,4) and a function of a derivative of the resistance with respect to the position of the particles (6) of the respective picture element (2).
4. A display panel (1) as claimed in claim 3 characterized in that the function is a sign function.
5. A display panel (1) as claimed in claim 1 characterized in that the electrical means (102) are able to generate for each picture element (2) the actual position information based on a capacitance between the first and the second electrode (3,4).
6. A display panel (1) as claimed in claim 1 characterized in that the electrical means (102) are able to generate for each picture element (2) the actual position information based on a capacitance between the first and the second electrode (3,4) and a function of a derivative of the capacitance with respect to the position of the particles (6) of the respective picture element (2).
7. A display panel (1) as claimed in claim 6 characterized in that the function is a sign function.
EP04701654A 2003-01-30 2004-01-13 Electrophoretic display panel Withdrawn EP1590782A1 (en)

Priority Applications (1)

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EP03100189 2003-01-30
EP03100189 2003-01-30
PCT/IB2004/050017 WO2004068449A1 (en) 2003-01-30 2004-01-13 Electrophoretic display panel
EP04701654A EP1590782A1 (en) 2003-01-30 2004-01-13 Electrophoretic display panel

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WO2008001288A1 (en) * 2006-06-26 2008-01-03 Koninklijke Philips Electronics N.V. Electrophoretic display devices
CN101479658B (en) * 2006-06-30 2011-03-09 皇家飞利浦电子股份有限公司 Electrophoretic display with homogeneously distributed electrically charged particles
WO2008018016A1 (en) * 2006-08-11 2008-02-14 Koninklijke Philips Electronics N.V. Electrophoretic display devices
CN102043602B (en) * 2009-10-09 2012-07-11 财团法人工业技术研究院 Multistable display system as well as image writing method of multistable monitor
KR101036334B1 (en) * 2011-01-12 2011-05-23 주식회사 나노브릭 Display method and apparatus using electrophoresis

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US20060139306A1 (en) 2006-06-29
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WO2004068449A1 (en) 2004-08-12
TW200500768A (en) 2005-01-01

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